As far as I can tell, it's just an emergency measure if the day chosen for the attacks happens to be election day. (It was in New York City on 9/11, and they had a provision to have the elections later rather than not having them at all when the city was in such chaos.) I'm of two minds, the first of which is going, "AAAAAAARGH." The other of which is going, "Um, if terrorists blow up the Capitol on election day morning, am I really going to be in any frame of mind to get to my polling place after work that night?"